Acrylic-based asymmetric and variable coupling ratio Y-branch plastic optical fiber coupler

Acrylic-based asymmetric and variable couplers have been developed using a single structured Y-branch design with a high-index-contrast waveguide taper and a void structure for fiber attenuation using the lateral displacement of two fibers. Device fabrication is performed by producing the device structure on an acrylic block using a computer numerical control (CNC) machine tool. The fabricated device has an excess loss of 5.85 dB, while the coupling ratios are 56.86 and 43.14% when the device is operated as a 3 dB coupler. In the asymmetric coupler mode, the coupling ratio ranges from 44.84 to 8.01% for port 1 and 55.16 to 91.99% for port 2. The excess loss of this device varies from 5.42 to 7.64 dB. In the variable coupler mode, the coupling ratio ranges from 10.09 to 32.88% for port 1 and from 89.91 to 67.12% for port 2. The excess loss of the device varies from 5.85 to 8.49 dB.     

Analyses for various doping structures of SOI-based optical phase modulator using free carrier dispersion effect

This paper highlights the study on various structure of silicon-on-insulator (SOI) optical phase modulators based on free carrier dispersion effect. The proposed modulators employ the forward biased P-I-N diode structure integrated in the waveguide and will be working at 1.55 μm optical telecommunications wavelength. Three kinds of structure are compared systematically where the p+ and n+ doping positions are varied. The modeling and characterization of the SOI phase modulators was carried out by 3D numerical simulation package. Our results show that the position of doping regions have a great influences to the device performance. It was discovered that the best structure in this work demonstrated modulation efficiency of 0.015 V cm with a length of 155 μm.     

Fabrication of 1×2 asymmetric plastic optical fiber coupler for portable optical access-card system

We proposed a simple low-cost acrylic and metal-based Y-branch plastic optical fiber (POF) splitter which utilizes a low cost optical polymer glue NOA63 as the main waveguiding medium at the waveguide taper region. The device is composed of three sections: an input POF waveguide, a middle waveguide taper region and output POF waveguides. A desktop high speed CNC engraver is utilized to produce the mold inserts used for the optical devices. Short POF fibers are inserted into the engraved slots at the input and output ports. UV curable optical polymer glue NOA63 is injected into the waveguide taper region and cured. The assembling is completed when the top plate is positioned to enclose the device structure and connecting screws are secured. Both POF splitters have an average insertion loss of 7.8 dB, coupling ratio of 55: 45 and 57: 43 for the acrylic and metal-based splitters respectively. The devices have excess loss of 4.82 and 4.73 dB for the acrylic and metal-based splitters respectively.     

Synthesis and fabrication of (1 − x)ZnAl2O4–xSiO2 thin films to be applied as patch antennas

Zinc aluminate compounds have been dispersed in silica matrix prepared by sol-gel method with different compositions for (1 ? x)ZnAl₂O₄–xSiO₂. Continuous stirring of ethylene glycol solution contained zinc nitrate, aluminium nitrate and silicon dioxide to produces gel precursor. Structural and morphological studies of (1 ? x)ZnAl₂O₄–xSiO₂ thin films were examined by field emission scanning electron microscopy (FESEM) and X-ray diffractometer (XRD) analysis. The FESEM images showed the spherical structures with porosity for (1 ? x)ZnAl₂O₄–xSiO₂ thin films. XRD analysis indicated that the crystallite size for (1 ? x)ZnAl₂O₄–xSiO₂ increased from 39.79 to 44.34 nm. Fourier transform infra-red analysis showed that the existence of H₂O molecules and the presence of nitrate group within the samples. Dielectric permittivity (ε _r ) of (1 ? x)ZnAl₂O₄–xSiO₂ samples were measured within frequency range from 1 Hz to 1 MHz. The dielectric permittivity, ε _r decreased as frequency was applied to the sample. The performance of the patch antenna can be measured using return loss analysis. The highest result shows that the patch antenna resonated at frequency 3.46 GHz and gives ?14.25 dB return loss bandwidth.     

Improved catalytic activity of Pt/rGO counter electrode in In2O3-based DSSC

A platinum/reduced graphene oxide (Pt/rGO) nanocomposite acting as a counter electrode (CE) was fabricated using a chemical bath deposition method for In₂O₃-based dye-sensitized solar cell (DSSC) via sol-gel technique. The report analyzes the morphological and electrochemical impedance spectroscopy of the annealing Pt/rGO films at 350, 400, and 450 °C. Micrograph images obtained from field emission scanning electron microscopy demonstrated the annealed films are highly porous. The energy-dispersive X-ray results show that the carbon atoms were homogeneously distributed on the film annealed at 400 °C. A good photovoltaic performance was exhibited with high photocurrent density of 8.1 mA cm⁻² and power conversion efficiency (η) of 1.68 % at the Pt/rGO CE annealed at 400 °C. The employed electrochemical impedance spectroscopy analysis quantifies that the Pt/rGO films annealed at 400 °C provide more efficient charge transfer with the lowest effective recombination rate and high electron life time, hence improving the performance of Pt/rGO CE.

     

Machining of acrylic-based Y-branch plastic optical fiber coupler with suspended waveguide taper

An acrylic-based Y-branch plastic optical fiber (POF) with a middle suspended waveguide taper has been developed. The suspended high index contrast waveguide taper structure has been designed in such a way that it is surrounded by air-cladding. Non-sequential ray tracing has been performed on the device giving an insertion loss of 4.68 dB and coupling ratio of 50: 50. The middle waveguide taper is constructed on the acrylic block itself without using any additional optical waveguiding medium injected into the engraved taper region. Fabrication of the devices is done by producing the device structures on an acrylic block using high speed computer numerical control (CNC) machining tool. Input and output POF fibers are inserted into this device structure in such a way that they are passively aligned to the middle waveguide taper structure. The device shows an insertion loss of 5.9 dB, excess loss of 2.9 dB and a splitting ratio of 50: 50.     

Performance and comparison of fiber vibration sensing using SAC-OCDMA with direct decoding techniques

Intensity modulated fiber vibrations sensing using Khazani Syed (KS) and Modified Quadratic Congruence Code (MQC) code for quasi distributed vibration measurement have been evaluated. The systems employed Spectral Direct (SD) Decoding for Spectral Amplitude Coding-Optical Code Division Multiple Access (SAC-OCDMA). SAC-OCDMA is adopted because of its enormous impact in dealing with Multiple Access Interference (MAI). The setup was carried out for three sensor points in three consecutive measurements. The performance of the sensing system with the KS and MQC codes were compared at the same weight and number of code sequence. It was observed that the applied vibration frequencies were obtained at the receivers and the signal employing MQC are received at slightly better power than KS code. However, KS code setup employed less number of components and therefore, reduce the cost and complexity of achieving quasi-distributed vibration sensing.     

Comprehensive uniformity analysis of GaAs-based VCSEL epiwafer by utilizing the on-wafer test capability

A comprehensive study of the uniformity of 850 nm VCSEL epiwafer grown by the MOCVD technique is presented. By utilizing the VCSEL planar structure, uniformity test is performed on-wafer directly, besides using the conventional photoluminescence technique. The VCSEL quantum wells are found to exhibit a peak emission wavelength of 839.5 nm. Also, the grown epiwafer is observed to exhibit a Fabry–Perot cavity resonance at 846.5 nm. Various VCSEL devices fabricated from the center to the edge of the VCSEL epiwafer show a similar trend towards the light–current and output spectral characteristics. However, the device existing near the epiwafer edge is observed to exhibit significantly different characteristics, which is attributed to the physical conditions of the device near the edge, and also the limitations of the epitaxial growth.